Planetary Health

Human health does not exist in isolation. Instead, it very much depends on the health of the planet we live on. Our climate, the richness of our ecosystems, and the quality of our air, water, and soil are all dependent on the complex systems of the world around us. When those systems are disrupted, the consequences can ripple into our daily lives, sometimes in ways we might not expect...including the spread of vectors like ticks and mosquitoes and the diseases they carry.

What Is Planetary Health?

Planetary health is a field that studies the connections between the health of us humans and the health of our natural world around us. The Planetary Health Alliance, a consortium of over 400 universities, NGOs, and research institutes, defines it as:

“The health of human civilisation and the state of the natural systems on which it depends.”

In practice, this means looking at how large-scale environmental changes (like deforestation, biodiversity loss, pollution, and climate change) affect human health outcomes in areas such as nutrition, infectious diseases, mental health, and other non-communicable health problems. It’s a lens that recognises the increasing difficulty of achieving healthy people on an unhealthy planet.

The concept builds on earlier ideas from One Health (which links human, animal, and environmental health), but broadens the scope to include the full Earth system: oceans, atmosphere, ice sheets, and all the living organisms that keep them in balance.

How Is Our Planet Changing?

The UK’s climate is already shifting. According to the Met Office, the top ten warmest years since recording began in 1884 are from the last two decades, and "four of the UK’s last five years now appear in the top five warmest years." Milder winters, longer growing seasons, and more frequent heatwaves are increasingly common. Rainfall patterns are also changing, with wetter winters and more intense downpours.

These shifts matter for vector-borne disease because ticks and mosquitoes are ectotherms, or cold-blooded organisms whose activity, development, and survival are mostly dictated by temperature and humidity. When the climate changes, so do the conditions that determine where, when, and how many vectors are present and active.

At the same time, land-use change is reshaping habitats. Urbanisation, agricultural intensification, and even rewilding projects all alter the mix of wildlife that vectors feed on, the vegetation they shelter in, and the contact points between animals, vectors, and people.

Changing Vector Distribution

As the climate warms, vectors are expanding into areas where they were previously absent, or at least rare. For the UK this means:

• Ticks at higher altitudes and further north. Ixodes ricinus, the UK’s most common tick, has been recorded at elevations and latitudes where it was not historically found. Milder winters allow more ticks to survive from one year to the next.
• Longer tick seasons. Ticks become active when the temperature exceeds about 4°C. Warmer springs and autumns extend the window of questing activity, increasing the time during which people and pets can be bitten.
• Invasive species establishing. Dermacentor reticulatus, previously confined to a handful of coastal sites, has been expanding in south-west England. Warmer conditions may accelerate this process and allow the tick to colonise new areas.
• New mosquito risks. Mosquitoes can respond quickly to warmer, wetter conditions. Species such as Culex modestus matter for surveillance because they are linked to wetland habitats and West Nile ecology in Europe. The invasive Asian tiger mosquito (Aedes albopictus) is already established in parts of southern Europe, and continued warming increases the chance of future UK establishment.

Changing Disease Risks

Climate and ecosystem change don’t just affect when and where vectors are found; they can also alter the diseases those vectors carry and how well those diseases are transmitted to wildlife, our pets, and ourselves.

In the UK, that means thinking about both ticks and mosquitoes together: tick surveillance remains the main public-health priority, while mosquito monitoring helps identify emerging risk early.

Temperature and pathogen development

Many pathogens go through a development period inside the vector before they can be transmitted to the next host. This is called the extrinsic incubation period (EIP). Higher temperatures typically shorten the EIP, meaning the pathogen matures faster and the vector becomes infectious sooner. For tick-borne pathogens, warmer conditions can also speed up the tick development, leading to faster life-cycle completion and more generations overlapping in a single season, increasing the potential for transmission amongst the tick population.

Host immunity and co-infections

Environmental stressors like heatwaves, poor air quality, and nutritional changes can weaken immune defences in both humans and wildlife. A deer population under nutritional stress, for example, may carry higher pathogen loads, creating a richer source of infection for feeding ticks. In humans, pre-existing health conditions exacerbated by climate change (such as respiratory or cardiovascular illness) can make vector-borne infections harder to fight off.

Biodiversity and the “dilution effect”

Healthy, species-rich ecosystems can sometimes reduce zoonotic disease risk. When many different animal species are present, ticks may be more likely to feed on hosts that are poor reservoirs for the pathogen, “diluting” the infection rate in tick populations. Loss of biodiversity can remove these buffer species, leaving highly competent reservoir hosts (such as small rodents for Lyme disease) as the dominant food source, which can increase infections in ticks.

UK Research Groups & Resources

A number of research groups across the UK are working at the intersection of environmental change, vector ecology, and public health. Here are some of the key organisations:

What Can You Do?

Planetary health can feel like an overwhelming topic, but individual actions do add up:

• Stay informed. Understanding how environmental change affects health is the first step. Pages on this site like Ticks, Prevent Bites, and Tick Removal give you practical knowledge.
• Report sightings. Citizen science helps scientists track changes in vector distribution. See our Citizen Science page for how to contribute.
• Support biodiversity. Wildlife-friendly gardening, supporting local conservation projects such as those listed by The Wildlife Trusts, and reducing pesticide use all help maintain the ecosystems that buffer us from disease.
• Reduce your impact and inspire change. Climate change is the biggest driver of vector range expansion. Making low-carbon choices from transport to diet matter, but advocacy is often the most effective for systems-level change. Joining climate campaigns through groups like The Climate Coalition can amplify your impact!

Further Reading

• Planetary Health Alliance — What Is Planetary Health?
• The Lancet Planetary Health — The Lancet
• WHO — Vector-Borne Diseases Fact Sheet
• Thomson et al. (2022) “Climate Change and Vector-Borne Diseases” — New England Journal of Medicine
• UKHSA — Health Effects of Climate Change in the UK
• Rocklöv & Dubrow (2020) “Climate change: an enduring challenge for vector-borne disease prevention and control” — Nature Climate Change
• United Nations Development Programme — Climate Change and Vector-Borne Diseases: A Looming Threat We Can't Ignore
• Royal Society — Reversing Biodiversity Loss